1. Field of the Invention
The present invention relates to the protection of the head and neck of an individual carrying heavy or dangerous equipment on his or her head. It can be applied especially to a helmet such as that of a pilot of an armed helicopter or aircraft where certain forms of equipment may aggravate the risks of injury to the wearer under particular conditions of use of the helmet.
A helmet such as that of the pilot of an armed helicopter does not only protect the head that it covers. It is a multifunctional device. It enables the mechanical protection of the skull as well as the protection of the ears, eyes and face. It also enables communication by auditory channels, assistance in viewing the environment and, if necessary, it supplies oxygen to the pilot. These functions are fulfilled by various types of equipment.
A helmet of this kind has a rigid body or shell that generally surrounds the peak, rear and side parts of the wearer's skull. The shell protects the skull from perforation. For modern helmets, it is often made of a highly resistant composite material.
The helmet also has an inner cap located between the rigid shell and the skull which is covered by the helmet. The cap is made of an absorbent material and protects the head by absorbing a part of the shocks received by the external face of the shell. Most usually, it is fixedly joined to the shell.
A system of auditory protection may be integrated into the internal cap, at the level of the wearer's ears.
The helmet may include a visor through which the helmet wearer can see his or her environment. The visor is usually retractable towards the peak of the skull. It forms a protective screen for the face when it is in the lowered position. The visor can also be provided with optical treatment on its surface for the optical protection of the wearer's eyes.
The function of sound communication can be obtained by a microphone placed in the vicinity of the mouth and earphones fixed close to the ears on the internal face of the cap.
Furthermore, the helmet commonly has equipment that provides display assistance. This equipment complements and/or replaces the direct view of the environment of the helmet wearer by means of visual information. The display assistance may include a system for superimposing a reticule, symbols or an image on the direct view in order, for example, to facilitate piloting, navigation or the designation of an object to be reached. The display assistance may also include a night vision device with sensors other than the human eye such as for example light intensifiers or infrared image sensors whose signals are processed to reconstruct an image of the night scene. The image is presented to the wearer's eyes. It provides night vision by complementing the direct view of the eye and/or by replacing it.
The visual information to be presented is for example displayed on a screen integrated into the helmet such as a cathode-ray tube screen or a liquid crystal screen. Optical devices also integrated into the helmet enable the presenting of information before the wearer's eyes. These devices generally comprise collimation means so that the wearer of the helmet can perceive visual information in the plane of the scene. The means used to present visual information to the wearer of the helmet constitute a helmet display device. The dimensions of the optical units integrated into the display device are reduced but their weight remains substantial.
The total mass of the multifunctional helmet fitted out with a display device becomes very great. It often exceeds half the mass of the bare head. And the distribution, in the helmet, of the weighty elements needed for all these functions and especially for display assistance is the result of a compromise made in order to meet various constraints. This display most often adds further weight to the upper part of the helmet and especially the part protecting the wearer's forehead.
Another relatively simple piece of equipment for night vision assistance consists in placing a night vision field glass before the eye. This field glass comprises a image-taking objective and a light intensifier. Thus, the eye sees an intensified image of the scene in the field glass. To free the observer's hands, the night vision field glass may be mounted on the helmet. It is generally fixedly joined to an arm that is attached to the helmet on the wearer's forehead. This position gives rises to added weight on the helmet towards the top and towards the front.
The center of gravity of the covered head fitted with a display assistance device is further away from the axis of rotation of the neck than the natural center of gravity of the bare head, because the helmet has an elongated lever arm.
And when the head thus covered undergoes high acceleration, for example when the helicopter being piloted by the helmet wearer crashes, the helmet fitted out with the night vision device exerts a moment on the pilot's neck. This moment is proportional to its total mass and to the square of the elongated lever arm. It is greater than the moment that would be exerted in the same example on the bare head.
Thus the neck, which can withstand a given acceleration on the bare head without harm, suffers serious injury when the same acceleration is applied to the weighed-down covered head for which the position of the center of gravity entails greater penalties.
2. Description of the Prior Art
To ensure the safety of the helmet wearer, one standard for helmets recommends a link between the helmet and a weighty element fixed to the helmet complying with the following characteristics: the link permits the ejection of the weighty element in the event of an emergency when the helmet is subjected to a longitudinal acceleration (i.e. along an axis perpendicular to the wearer's face) the value of this acceleration ranging from 100 m/s.sup.2 to 150 m/s.sup.2. The prior art teaches us the use of a link formed by a retractable bolt using a spring that gets compressed when the acceleration goes beyond a threshold. When the helmet at rest undergoes no acceleration, the initial tension of the spring takes account of the mass to be ejected and the acceleration threshold desired to activate the ejection.
The ejection lightens the covered head by the jettisoned mass. It thus reduces the force of inertia of the covered head and the moment of this force applied to the joint of the neck. The ejection provides for a protection of the neck. However, this protection taught by the prior art is insufficient.
First of all, the protection during a frontal shock is efficient only if the shock undergone by the helicopter is sufficiently strong. In the event of a weaker frontal shock, the link is maintained, the mass is not ejected and the neck may be damaged by a shear stress.
Furthermore, the ejection is not ensured when the shock is not frontal, for example if the helicopter crashes vertically during stationary flight or again in the event of a lateral crash due to the gyroscopic torque of the rotor of the helicopter.
Furthermore, in the case of a weighty piece of equipment installed beneath the visor, the protection of the neck is provided by the ejection of the assembly comprising the weighty equipment and the visor but the ejection of this assembly deprives the wearer's face of the mechanical protection provided by the visor and often reduces the protection of the forehead. This protection of the neck leads to a reduction in the protection, against impacts, of a part of the head. It increases the risk of injuries to the head during an accident.
The problem lies in making a helmet that provides better protection for its wearer's head and neck especially in the case of emergency when one or more elements of the helmet become an immediate danger to the wearer of the helmet.